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The present invention relates to devices for generating and measuring electrical outputs, and more particularly, to voltage and current sources for generating and measuring electrical outputs having variable current and/or voltage characteristics, wherein the outputs are provided to electrical devices being evaluated by a testing system.
A testing system for testing electrical devices such as integrated circuits typically includes a test head connected to a mainframe system by a section of cable. The test head may also be mounted to a manipulator arm to provide a mechanical advantage to assist the user in moving the test head. The device under test (hereinafter referred to as xe2x80x9cDUTxe2x80x9d) mounts on test head such that electrical leads of the DUT are electrically coupled to corresponding test leads of the test head. In general, the mainframe system evaluates the DUT by providing a variety of signals to the DUT and evaluating how the DUT responds to those signals. It is also useful to ascertain how the DUT alters the signals provided by the mainframe system, especially for test signals whose voltage and/or current characteristics exhibit a wide dynamic range. For example, the mainframe system may arrange to provide a 5 volt test signal to an input of the DUT, then evaluate the state of the DUT output signals, along with the current draw of the DUT on that 5 volt test signal. How the DUT alters the test signal can provide significant information regarding the functionality of the DUT. In some test situations, a DUT may require a particular voltage or current input in addition to the control signals. For example, a semiconductor switch may be used to control the flow of a relatively large amount of current for a motor or other high current sink. Such a semiconductor switch may not only include control inputs and diagnostic outputs, but also an input that receives the relatively large electrical flow from a high power source, and an output that directs the electrical flow to the current sink. When the DUT includes this sort of device, the test system must not only supply low level control signals, but also higher power inputs.
In many prior art test systems, all such test signals between the mainframe system and the test head must travel via the section of cable connecting them. The testing system also generally supplies operating power to the DUT. Many such systems include DUT power supplies in the mainframe so that power delivered to the DUT travels through the cable. During the testing procedure, advanced, state-of-the-art DUTs often transition from a standby mode to an active mode, such that the DUT current draw can vary by a factor of 500 or more (e.g., 0.02 A to 10 A). These DUT power transitions can occur in just a few clocks cycles, which translates to a large current slew rate. Hereinafter, the term xe2x80x9cvoltage and current sourcexe2x80x9d is used to generally describe a power supply (i.e., a continuous power source), a relatively high capacity voltage and current source (i.e., a pulsed power source, such as that described above for driving a semiconductor switch). In prior art systems, these two functions are typically implemented by two individual components because of the unique nature of each of the functions, thus affecting the size, power requirements, cost and reliability of the overall test system.
To provide convenient access to the DUT, as well as relatively free manipulation of the entire test head, the section of cable between the test head and the electrical instruments residing within the mainframe may be in excess of ten feet. A long cable corresponds to large series inductance, which introduces a low pass filter (hereinafter referred to as xe2x80x9cLPFxe2x80x9d) between the power supply and the DUT. The LPF created by the cable removes high frequency components, so that the transition edges of signals transmitted via the cable are effectively slowed. Thus, the practical consequence of the cable being between the test head and the mainframe is that the DUT does not receive a true representation of the signal that the mainframe generates. In prior art systems, the location of the voltage and current source, especially one having a wide dynamic range (with respect to voltage and/or current; e.g., current transitions from microamps to amps), is generally irrelevant, because the bandwidth (hereinafter referred to as xe2x80x9cBWxe2x80x9d) of most such devices isn""t high enough to be limited by the LPF. In other words, typical prior art voltage and current sources simply can""t keep up with the current transition requirements of modem DUTs, so no motivation exists for placing such a device closer to the DUT.
Some prior art systems include a voltage and current source at an intermediate location between the mainframe and the test head, often somewhere nearer to the test head than the mainframe. A cable connecting the voltage and current source to the test head is present, but it is typically significantly shorter than the ten feet as described above. Although such sources are specifically designed for higher bandwidth, the cable still imposes limitations on the test signal transitions.
There are a number of factors that have traditionally discouraged mounting voltage and current sources within a test head, nearer to the DUT, thus reducing the intervening cable length. One of these factors includes cooling considerations. A voltage and current source capable of providing the amount of power that the DUT requires typically dissipates a significant amount of heat. This dissipated heat adversely affects the DUT, along with the associated electronics, if the heat is not efficiently removed from the test head. Traditional, air based cooling systems are generally not efficient enough to remove this heat, so designers often locate these power supplies outside of the test head.
Another factor discouraging voltage and current source in the test head is that a power supply capable of providing the amount of power that the DUT requires typically occupies a significant amount of physical space. This is especially true for linear mode power supplies, which are often used for DUT supplies because of the high quality regulation they provide. Thus, designers typically conserve test head space by locating the DUT power supply outside of the test head. Until very recently, the current input requirements of integrated electrical devices have been relatively modest, typically within a few amps. As more functionality is added and clock rates increase, the current input requirements of integrated electrical devices are increasing dramatically. Such high capacity continuous current and voltage sources are typically physically large, and so can not be included in the limited space of a test head. In some applications, large, continuous output voltage and current sources are used for their high output capability, even though the nature of the application does not require a continuous output. Further, a relatively recent practice is to design integrated electrical devices with integrated semiconductor power switches. Thus, such a device requires the same high current output source that a stand-alone semiconductor switch (described herein) requires.
Another factor weighing in favor of locating the voltage and current source outside of the test head is essentially organizational in nature. The group that tests highly integrated very large scale integration (hereinafter referred to as VLSI) digital devices is usually physically separate from the mixed signal test group. Although the VLSI group often encounters the aforementioned fast transition problem, they do not have the analog expertise to solve the problem. Conversely, although the mixed signal group possesses the expertise to solve such a problem, they are typically not aware of the problem.
A category of prior art voltage and current sources can provide a predetermined output profile in terms of voltage, current, or a combination thereof. However, a disadvantage of such existing voltage and current sources is a significant lack of precise control over characteristics of the output profile, e.g., timing. Such prior art sources cannot be digitally synchronized precisely to other events occurring in the host system.
Further, prior art voltage and current sources located within the test head do not provide means of direct repetitive sampling of the output signals (e.g., current and voltage). Typically a user can accomplish repetitive sampling only by placing a suitable external measurement device at the voltage and current source output and sampling the output at predetermined intervals.
It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.
The foregoing and other objects are achieved by the invention, a test system for testing at least one electrical component, comprising a test head that includes a mounting assembly for removably attaching the electrical component, and a plurality of test ports for electrically coupling to the electrical component. The test system further includes a voltage and current source being disposed within the test head, constructed and arranged so as to provide at least one electrical output, through an interface assembly, to the electrical component. The electrical output has a voltage magnitude within a predetermined voltage range and has a current magnitude within a predetermined current range. The voltage and current source further analyzes the electrical output so as to detect and measure one or more changes to the electrical output caused by the electrical component. The voltage and current source also receives and analyzes a plurality of response signals through the interface assembly from the signal ports of the electrical component. The electrical output is characterized by a plurality of transitions and a predetermined repetition rate between consecutive the transitions.
In another embodiment of the invention, the transitions include current transitions.
In another embodiment of the invention, the transitions include voltage transitions.
In another embodiment, the voltage and current source is disposed substantially adjacent to the electrical component, so as to minimize a length of the power interface assembly.
In another embodiment, the power interface assembly includes a cable assembly.
In another embodiment, the power interface assembly includes a printed circuit board assembly.
In another embodiment of the invention, the power supply is cooled by a liquid-based cooling system.
In another embodiment, the electrical output provided by the voltage and current source is characterized by an output profile with respect to time.
In another embodiment, the output profile includes variations in an output current.
In another embodiment, the output profile includes variations in an output voltage.
In another embodiment of the invention, a sequencer controls the electrical output such that the power output profile includes a contiguous series of discrete steps.
In another embodiment, the sequencer is initiated by an external trigger source from an associated control system, synchronous to a master reference clock.
In another embodiment, the sequencer controls an amplitude and a duration of each of the discrete steps.
In another embodiment of the invention, the sequencer includes a plurality of output profiles, one of which is selected by an associated control system.
In another embodiment, the test system further includes a measurement output for providing an electrical measurement signal representative of a characteristic of the electrical output.
In another embodiment, the electrical output is periodically sampled at a sampling rate, such that the electrical measurement signal includes a sequence of digital words.
In another embodiment, the voltage and current source is electrically coupled to a mainframe system such that the voltage and current source functions as a remote extension of the mainframe system, and the mainframe system originates the electrical output, analyzes the electrical output, and analyzes the response signals.
In another embodiment, the voltage and current source includes an energy storage element, wherein the voltage and storage source directs energy from the storage element to the at least one electrical output.
In another embodiment, the energy storage element is subdivided into a first portion and a second portion. The first portion resides within the test head and the second portion resides outside of the test head.
In another aspect of the invention, a test system for providing a repetitive, predetermined signal waveform to an electrical component comprises a sequencer constructed and arranged to produce a time varying control signal, corresponding to the predetermined signal waveform, as a result of an input trigger signal. The test system further includes a voltage and current source constructed and arranged to produce an electrical output that is a predetermined function of the control signal. The voltage and current source is electrically coupled to the electrical component so as to deliver the electrical output to the electrical component.
In another embodiment of the invention, the predetermined signal waveform includes a predetermined sequence of current transitions, so as to establish a contiguous series of current steps.
In another embodiment, the predetermined signal waveform includes a predetermined sequence of voltage transitions so as to establish a contiguous series of voltage steps.
In another embodiment, the sequencer is initiated by an external trigger source from an associated control system, synchronous to a master reference clock.
In another embodiment, the sequencer controls an amplitude of the predetermined signal waveform and a duration of each of a plurality of step intervals within the signal waveform.
In another embodiment, the sequencer includes a plurality of predetermined signal waveforms, one of which is selected by an associated control system.
In another embodiment, the test system further includes a measurement output for providing an electrical measurement signal representative of a magnitude of the predetermined signal waveform.
In another embodiment, the predetermined signal waveform is periodically sampled at a sampling rate, such that the electrical measurement signal includes a sequence of digital words.